1. Field of the Invention
The present invention relates to a windows-based power management method, and more particularly to a windows-based power management method for optimizing the power distribution in a portable device.
2. Description of the Prior Art
The typical power source of a notebook computer is a battery when the notebook computer is not connected to an external power outlet. The obvious drawback of using a battery as the power source for a notebook computer is that a battery can only provide a limited amount of power. Because of the limited amount of power of a battery, the usage time of a battery-powered notebook computer is variable, depending on the power consumption of the electronic devices used in the notebook computer.
Generally, one of the most straightforward and simplest ways to extend the usage time of a battery-powered notebook computer is to substitute the electronic device or component used in the notebook with an alternative that consumes less power while providing the same function. For example, most notebook computers employ a TFT (thin film transistor) LCD as their display screens, which dissipate more than 70% of the power supplied by the battery. However, the usage time of a battery-powered notebook computer can be extended obviously by using an organic EL display (organic electroluminescent display) instead of a TFT (thin film transistor) LCD.
Another approach to extend the usage time of a battery-powered notebook computer can be attained by using a central processing unit (CPU) chip with a low threshold voltage and thin oxide gates. In this case, the usage time of a battery-powered notebook computer can be prolonged by making a trade-off with the performance of the CPU. Another approach to extend the usage time of a battery-powered notebook computer is to use a non-volatile memory such as a flash memory instead of a hard disk. Non-volatile memory consumes less power because it does not consume a considerable amount of power as a hard disk when it is starting or stopping operation.
Though the above-mentioned way is very simple, its implementation is not always practical. Generally the main reason is due to the fact that the technology being essential to these alternatives is still under development or these alternatives are not so cost-effective as to replace the widely used electronic device. Taking the organic EL display for example, there are still many technical problems that are needed to overcome. As for the flash memory, the consideration on cost prevents it from replacing the hard disk because it is much more expensive to adopt a flash memory in place of a hard disk. As a result, designers of portable electrical devices have to employ other solutions to solve the problem of how to extend the usage time of a battery-powered notebook computer.
Another approach to extend the usage time of a battery-powered notebook computer is to use electronic devices with low power consumption. For instance, the most common example is to power off the hard disk of a notebook when it is not accessing data. Another example is to direct the processor of notebook to operate in a lower voltage. Power is saved in this way because the power consumption in a clock cycle is proportional to the square of the operation voltage. As a result, the power consumption of the processor is reduced efficiently by adjusting the operating voltage of processor dynamically, thereby extending the usage time of the notebook computer without needing extra time slots of the processor.
In addition to the solution by using electronic devices with low power consumption, another way for reducing the power consumption is to utilize a time-sharing system that schedules power management. In other words, under a time-sharing system the operating system takes the demands of each program into consideration and allocates different amounts of power to the processor when it runs different programs. When a first-come first-served (FCFS), shortest job first (SJF), priority scheduling, round-robin scheduling, multilevel queue scheduling, or multilevel feedback queue scheduling is used, the allocated CPU time slots for the programs that are sorted into the same category are fixed (note, however, deterministic modeling or scheduling evaluation of a queuing model applies a different standard for scheduling based on the characteristic of CPU, for example, the utilization of CPU, the throughput of CPU, and the waiting time of CPU). For example, most application programs can be divided into the following categories: soft real-time application programs such as a video player program or a music player program, interactive application programs such as a web browser, and batch application programs such as FTP (file transfer protocol) client software. According to the execution cycle of a program, the operating system allocates different time slices for CPU to execute different tasks in order to save power while avoiding a noticeable reduction in efficiency. When a program is being executed, the operating system also provides a plurality of time slices for CPU to execute different programs.
The typical power management method of portable devices, such as a battery-powered notebook computer, provides the processor with time slices to programs according to time that program needs to be accomplished. However, this kind of power management method does not involve adjusting the power supply requirements with time. This can pose a problem when users execute several tasks on a portable device. Typically, the task which is of a major concern to the user and which has to be accomplished as quickly as possible is the task running in an active window. It would improve efficiency if the resources can be transferred from low priority tasks, which are not to be executed momentarily by processor, to the task running in active window. The present invention can satisfy these needs.